Muscle exercise may be characterized as follows:
(I) Active exercise wherein the subject exerts the muscular force producing the exercise motion.
(II) Passive exercise wherein the subject does not exert the muscular force producing the exercise motion.
(A) Concentric contraction wherein the muscle shortens while the subject is contracting against external resistance.
(B) Eccentric contraction wherein the muscle lengthens while the subject is contracting against external resistance.
(1) Isotonic contraction or exercise wherein the external resistance force remains constant during a dynamic contraction, so that the speed of the exercise motion varies in response to the magnitude of the muscular force.
(2) Isometric contraction or exercise wherein the length of the muscle is held constant during a static contraction, so that the external resistance force varies in response to the magnitude of the muscular force.
(3) Isokinetic contraction or exercise wherein the speed of the exercise motion is held constant during a dynamic contraction, so that the external resistance force varies in response to the magnitude of the muscular force.
The present invention is primarily concerned with active, concentric, isokinetic exercise. However, it will be apparent that counter motions provide eccentric contraction as well.
It is well known that the overall conditioning of an athlete is very important. For this reason, many athletes lift weights, run, stretch and generally play a variety of sports to remain in good condition. Additionally, numerous practice sessions wherein the specific movements important to the athlete during his particular athletic contest are practiced over and over again many times a week. For example, in baseball a hitter may take batting practice for a period of time each day. Similarly, a football kicker will simply kick a ball many times each day. Or, a hockey player will practice numerous slaps shots day after day. Such practicing improves coordination and timing but another important aspect of the practice is the strengthening of the specific muscles which are used during the specific movement.
In a rehabilitation sense, U.S. Pat. No. 4,337,050 shows a recognition of the importance of exercising specific movements for rehabilitating a person to do the types of movements that he will do when he returns to his employment following an injury. The apparatus disclosed, however, provides only for use of various tools for rotation about a fixed axis. U.S. Pat. No. 3,567,219 shows an earlier version of similar apparatus. It provides for exercising by pushing or pulling an arm about a fixed axis.
With respect to sports, U.S. Pat. No. 2,134,451 shows the use of a baseball bat or a tennis racket attached to a weight hanging from a pulley system. Muscles are exercised to the extent that movement of the bat or racket in one direction requires a force equivalent to lifting the weight. U.S. Pat. No. 3,462,156 shows a similar idea for a golf club wherein the handle is connected with a cord to a retraction reel. U.S. Pat. No. 4,328,964 provides a more recent version of the same concept in that elastic ropes are fixed at one end and connected to various athletic instruments at the other end. Movement in one direction away from the fixed end of the ropes is resisted.
The devices of this latter group of patents provide a resisting stress for some of the muscles used during a particular athletic movement, but the design of the devices prevents the type of movement which would really be used during an athletic event and, furthermore, the devices provide resistance only in one direction while practicing any type of movement.
U.S. Pat. No. 3,738,661 discloses a golf exercising device which allows the exercising person to swing somewhat similarly to his actual golf swing. The device has an arm rotatable about an axis. The arm has a flexible portion ending in a handle. The device, however, is limited to rotating the arm about the axis and, thus, makes any swing rather circular. The flexible portion of the arm at least allows for the wrists to turn. Although many of the muscles used during a golf swing are undoubtedly exercised by this machine, the form of the swing is dictated and probably harmful of actual improvement of golfing skill.
U.S. Pat. No. 4,211,418 shows a different approach wherein an apparatus has a pair of rods at approximately 90 degrees with respect to each other. A rotational axis bisects the angle between the rods. The exercising person places a golf club in front of one rod and rotates the apparatus as the club is moved into a back swing. When the person stops, the apparatus rotates the rods 180 degrees so that the other rod makes contact with the front of the golf club. Then the person makes his foreswing while pushing the rod throughout the swing. Although the apparatus is less constraining than the device of the previously described patent, there is an artificial lag time at the top of the back swing and there would appear to be some safety problems with respect to the swinging rods, especially if the golf club were to slip off the rod or if the swinging rod made too fast an impact with the golf club as the person is at the top of his back swing.
It is clear that many exercising devices have been devised, some quite crude while others are more complex. None, however, offer the athlete the opportunity to practice in both forward and reverse directions good dynamic form while stressing the exact muscles used for a particular athletic movement.